So what was it about your cousin's method that sold you? Like, were they doing something totally different with the grind or water temp, or was it just that the coffee tasted way better than you expected from a plastic plunger thing? I always hear people tweaking their process but never what actually changes someone's mind on the spot.
Honestly it was watching him use a much finer grind than I ever tried, with water just off the boil. I always assumed the plunger needed coarse grit and cooler water to avoid bitterness, but his cup was shockingly clean and bright. That one demo totally flipped my view on what that "plastic plunger thing" could even do.